Systems for distributing electric power from generating facilities to users such as businesses and residences usually employ transformers to reduce voltage. Relatively low electrical potential delivered to residential and some business users is typically around 120 to 600 volts, whereas electric power is usually distributed at much higher voltage from generators to transformers located in the vicinity of users. Transformers are thus used to step voltage down from relatively high primary voltage to relatively low secondary voltage. Electric power at secondary voltage is typically distributed from transformers to meters, with one transformer typically serving multiple meters.
Underground primary power configurations presently in use for underground electrical power distribution typically include a junction box or similar device that provides a means for continuing a primary power line downstream in one or more directions, in addition to providing primary voltage to a transformer and a junction box or similar device. Transformers typically provide one source to extend primary voltage to a downstream primary device.
Maintenance or replacement of an underground transformer requires that it be de-energized by interrupting primary power to the transformer. Typically, with devices currently in use, a transformer is de-energized by disconnecting an upstream connection at primary voltage. Such a primary voltage connection sometimes comprises a loadbreak elbow and a bushing at a junction box or a transformer. Interrupting power by disconnecting a loadbreak elbow from a bushing not only de-energizes the transformer being modified, but usually interrupts power downstream as well. Thus, downstream electric power users have electric power interrupted, as do those users supplied by the transformer being serviced or modified.
Primary connections in transformer assemblies typically comprise loadbreak elbows adapted to disconnect from bushings in order to interrupt power to the transformer primary side. The loadbreak elbows are also adapted to readily reconnect with the bushings in order to reestablish primary power to the transformer. Loadbreak elbow and bushing connections are generally preferable to switches for use on the primary side because high voltage switches are vulnerable to arcing and other problems associated with interrupting high voltage circuits. Primary loadbreak elbows that have been disconnected from a transformer, but which are still energized, are challenging to store safely.
Line tools such as a shot gun enable electric utility workers to disconnect and maneuver high voltage loadbreak elbows without excessive danger caused by exposure to high voltage. Loadbreak elbow and bushing connections are thus widely accepted devices for providing relatively safe primary power connections in transformer assemblies.
In addition to requiring interruption of downstream primary power when de-energizing a transformer for maintenance or replacement, present day transformer design requires that connections between service wires and a transformer be electrically and physically disconnected at a secondary block of a transformer assembly, particularly where a transformer or secondary blocks are being removed or replaced. Such interruption frequently requires disconnecting three separate secondary or service wires for each meter, requiring disconnection of as many as 18 or more secondary or service wires before removing one transformer. Disconnecting and then reconnecting secondary or service wires for each meter is inefficient; it is frequently time consuming and tedious.
Underground primary power line configurations currently in use typically have a transformer and junction box positioned at separate locations. Thus a single transformer and single junction box sometimes requires two utility boxes in close proximity to each other, which can be unsightly.
In summary, underground primary power line configurations currently in use require that downstream primary service be interrupted when the transformer to be serviced or changed-out is de-energized. Moreover, a transformer in a typical contemporary assembly must be disconnected from an upstream junction box, transformer, or switch device and from individual secondary or services wires at a secondary block, in order to remove or replace the transformer. Having to replace both transformer connections and a plenitude of secondary block connection increases maintenance time, which increases the interval during which a transformer is de-energized. Downstream users can be deprived of electric power during this interval, if transformer is not in a loop configuration. Finally, underground primary systems may consist of transformers and junction boxes disposed at separate locations, sometimes requiring two utility boxes in close proximity of each other. Such configuration is an inefficient use of space and material, and is unnecessarily aesthetically disruptive.